Republican Frontrunner Donald Trump has started wearing a bulletproof vest amidst safety concerns as the US election race continues. According to sources close to Trump's campaign, he began wearing the body armour several months ago.

The added weight of wearing a bullet proof vest through long and often violent rallies has left the billionaire "tired" by the end of most of the events, said the source. The result is an explanation of why Trump is left "sweaty and spent after events." "People who know Trump say they've never seen him so tired," reported the New York magazine.

Earlier in March, a Trump rally took a violent turn when a protester attempted to take to the stage in Ohio. Secret Service agents reportedly came to the Republican frontrunner's rescue. The billionaire tycoon was also subjected to a cyber attack when hackers affiliated with the Anonymous collective launched several distributed-denial-of-service (DDoS) attacks on websites related to the presidential hopeful.

Trump had warned earlier in March that riots will possibly erupt if he is denied a presidential nomination. "I think you'd have riots. I think you'd have riots," said Trump during an interview on CNN on 16 March. "I'm representing a tremendous many, many millions of people."

A Trump supporter had later justified the riots. Speaking to CNN's Wolf Blitzer, Scottie Neil Hughes said: "It's not riot as in a negative thing like what we've seen in the past, it's the fact that you have a large amount of people that will be very unhappy ... I know they would not resort to violence ... However, they would make sure their voices are heard, that they can't be ignored."

On 5 April, Trump will face rival Ted Cruz in Wisconsin's primary with 42 delegates up for grabs. Trump is currently leading with 736 delegates, followed by Ted Cruz with 463 and Ohio Governor John Kasich with 143.